The present invention relates to a hand circular saw with a swinging protective hood and with a cutting depth adjusting device.
Hand circular saws of the above mentioned general type are known in the art. One of such saws is disclosed for example in U.S. Pat. No. 4,856,394. A hand circular saw disclosed in this reference and having a swinging protective hood, a cutting depth adjusting device and a miter angle adjusting device is shortly called a standard hand circular saw. The cutting depth is determined by the distance of projection of the saw blade under the base plate. It is adjusted by turning the saw blade on and off relative to the base plate about an axis extending parallel to the rotary axis of the saw blade in turning bearings or guides, and arresting the saw blade in the desired position by clamping means relative to the base plate or the cutting depth guiding bracket. The hand circular saw is supported on a workpiece by means of the base plate, and therefore the angular and height position of the saw blade relative to the workpiece is controlled better than in the case of free suspending not supported systems. The adjusting devices provide a high degree of freedom for the saw blade with a simultaneous accurate guidance relative to the workpiece.
The standard hand circular saws are predominantly utilized for displacement sawing and rarer for plunge sawing. For the plunge sawing special saws are developed which have no swinging protective hood. Their saw blade is turnable back and forth together with the motor or transmission housing relative to the saw blade housing and the base blade for adjusting the cutting depth. The cutting depth adjustment is not arrestable on safety reasons, but instead is limited by abutment means. In some cases because of the safety reasons, instead of the swinging protective hood, spring means of the saw blade are pressed to the position of the minimal cutting depth. The safety reasons relate basically to the injury danger for the operator in view of the saw blade projecting downwardly of the base plate, when the hand saw blade is removed from the workpiece and the saw blade does not simultaneously retreat above the base plate. The so-called plunge saws, in view of the absent cutting depth clamping, are less favorable for displacement sawing than the standard hand circular saws.
During displacement sawing with the standard circular saws the turning bearing and guides in the case of the fixedly clamped cutting depth adjustment are loaded only by the weight forces of the saw, or in other words very little. Moreover, because of the clamping an especially stable connection is obtained between the housing and the cutting depth guiding bracket or the base plate, and therefore the saw blade during the displacement sawing remains stable in its desired plane.
During plunge cutting with the standard hand circular blades, in addition to the weight forces also the reaction forces act on the cutting depth adjusting device through the tool engagement in the workpiece. The clamping of the housing relative to the cutting depth guiding bracket is prohibited here, since otherwise no variable cutting depth adjustment required for the plunge cutting will be possible. Thereby the guidance of the housing relative to the base plate or relative to the cutting depth guiding bracket is less stable than during the displacement sawing and the cutting depth guiding bracket is loaded higher than during the displacement sawing. There is here the danger that the saw blade during the plunge cutting can displace or tilt from its plane perpendicular to the base plate. Deviation from the required position can lead to canting of the saw blade in the sawing gap, and excessive chips are removed.
Since the plunge saws with standard hand circular saws are now the exception and good plunge saws are provided, the manufacture of the standard hand circular saws paid relatively little attention to the quality of the guide between the housing and the base plate or the cutting depth adjusting bracket. Thereby a high quality plunge sawing with the standard hand circular saws is not possible. In particular the plunge sawing with a miter angle of approximately 45.degree., the forces acting between the housing and the base plate during feeding in the plunge cutting influence the position of the saw blade and thereby the working output so much that practically an accurate plunge cutting was not possible.
For better understanding of the invention, substantial adjustment steps on standard and circular saws during displacement and plunge sawing are clarified. The following adjustment steps are required during the displacement sawing:
The hand circular saw is placed with the base plate on a fixed substrate; PA1 The clamping screw for arresting of the cutting depth is released; PA1 The housing is turned up and down relative the base plate for obtaining a nominal cutting depth and arrested by tightening of the clamping screw; PA1 The base plate is placed on the edge of the workpiece and the closed swinging protective hood abuts with its end side against the edge of the workpiece; PA1 The hand circular saw with the cutting side is brought in alignment with a predetermined marking line on the workpiece; PA1 The motor is turned on and the displacement sawing starts by a horizontal displacement of the saw, while the swinging protective hood is open by abutting of its end side against the workpiece edge. PA1 A clamping screw for arresting of the cutting depth is released; PA1 Adjustment of the negative cutting depth is performed by upward turning of the housing with a saw blade relative to the base plate so that the saw teeth facing the base plate extend toward it; PA1 The cutting depth abutment is adjusted and arrested for limiting the cutting depth; PA1 The swinging protective hood is open; PA1 The base plate is placed on the workpiece; PA1 The marking line and the cutting side are brought in alignment; PA1 The motor is switched on; PA1 The operating saw blade is lowered into the workpiece until the adjusted cutting depth, or in other words until abutment of the housing against the cutting depth abutment; PA1 The clamping screw is arrested.
The following adjustment steps are required for the plunge sawing with the hand circular saws having a swinging protective hood:
The plunge cutting process is finished, and in this position displacement cutting can continue.